Dispatchers for the Evansdale police and Black Hawk County Sheriff's Office said crews would renew efforts to find the girls on Monday. Authorities have been dredging the lake and interviewing family, friends and registered sex offenders who live in the area.

The mothers of both girls said they were trying to stay strong.

"Today I'm feeling pretty good," Misty Cook-Morrissey said Sunday. "Sometimes, when you think about it, you wonder if they're dead somewhere, but you try to push those thoughts out of your mind."

Cook-Morrissey said she was grateful for the community support in Evansdale, a Waterloo suburb in northeast Iowa.

"It's been good talking to people," she said. "It keeps your mind off of what's happening."

Black Hawk County Sheriff's deputy Rick Abben said officials were "grasping for straws."

Cook-Morrissey said her daughter might have tried to swim at the lake, despite a swimming ban. She said the family swims at another nearby lake regularly, and described Lyric as a good swimmer.

Elizabeth's mother, Heather Collins, said it's rare for her daughter to venture too far from home, but she may have been persuaded by her older cousin.

"We've talked about that before," Collins said "We've told them they're too young to go far."

Misty Cook-Morrissey and Heather Collins are sisters.

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